The present invention relates to a control system which is operated by means of a power supply system derived from a supply voltage switched to a load. It allows a controller to be kept in operation without any need of an additional wire or batteries. It is particularly suited for electronic thermostats connected to electrical loads, allowing the connection of an electronic switch and a temperature controller by means of only two wires.
The electronic thermostats currently on the market use electronic switches such as thyristors or triacs to connect or disconnect the AC line with a heating element. Such systems require three wires connected to the thermostats to be operative. Two wires energize the thermostat from the AC line voltage, the first wire being connected to one extremity of a heating element whereas the second extremity of the heating element is connected to the other extremity of the electronic controller.
According to the invention, only two wires are needed for connecting the electronic thermostat to a heating element. A regulating system provides a stabilized power supply which is used for activating the electronic controller in a continuous manner. The stabilized power supply is regulated during the periods during which the heating element is not activated. However, if the heating element must be activated for a long period of time, an electronic device disconnects the AC line from the heating element when necessary and during a certain number of alternating cycles to accumulate energy and maintain the stabilized power supply at an acceptable standard of operation.
The present invention prevents the use of a battery as it is the case, for example, in the Canadian patent no. 1,035,448 (LAMBERT) granted on July 25th, 1978, or the use of an emergency battery as proposed in the French patent no. 2,491,692 (KABAT) published on Apr. 9th, 1982. In many cases, the present invention prevents the need for installing a third wire in walls where the system in place provides only two wires. It also prevents the need for modulating control pulses over the power supply wires energizing the thermostat, which produces several transients on the line. The present invention is different from the bridge configurations suggested in the Canadian patent no. 1,217,544 (CROSS et al.) granted on Feb. 3rd, 1987 and wherein the thermostat is connected directly on the radiator. It can also be used in cooling or heating systems such as described in the Canadian patent no. 797,079 (RAY) granted on Oct. 22nd, 1968.
The present invention is also different from the inventions based on the method known as "phase angle control" and that is mentioned in the patents of Kammerer et (U.S. Pat. No. 4,745,300), Evans (U.S. Pat. No. 4,504,778), Kompelien (U.S. Pat. No. 4,328,528), Goldstein (U.S. Pat. No. 4,274,045. and Sankusu et al (Japanese patent no. 47 129).
The method used in the above mentioned patents comprises a step of interrupting the supply of the load during a certain portion of the phase of the alternating half-cycle. It is the level of a voltage threshold value or of a predetermined angle that determines the phase at which the supply is ended, and at which the supply of the load is triggered.
This method has several drawbacks that limit its practical realization. The interruptions of the power supply produce many transients on the line, and emit electromagnetic interference. The interference or the transients are important in so far as the ohmic value of the load is low. Moreover, the current used to supply the controller is dependant upon the ohmic value of the load and consequently, the energy available for the controller depends on the impedance of the load.
Another drawback results from the fact that the commutation phase of each half-cycle being relatively low, the energy accumulated for supplying the controller is limited to a low value which limits the consumption, and therefore the applications of the controller.
According to the present invention, the commutation of the supply of the load is synchronized at the zero crossing of the sector voltage, and allows a supply of large power loads without producing transients or interferences, and to maintain a sufficient amount of energy for the needs of the controller. Therefore, the present method does not depend upon the voltage level of the threshold or the phase of the sector power supply.
The present invention also differs from the U.S. Pat. No. 4,678,985 of Moskin, which necessitates the use of a transformer. The present invention also differs from the U.S. Pat. No. 4,374,321 of Cunningham Jr et al., which relates to a photocopying machine in which the interruptions of the power supply are not used for supplying the controller. The present invention also differs from U.S. Pat. No. 3,881,118 of Forest in which there is no control of the number of cycles used to charge the controller. The invention disclosed in U.S. Pat. No. 4,554,439 of Cross et al., in which the two wires available for the controller are for the power supply only when the load is included in the controler, the load being in fact connected in parallel with the controller also differs from the present invention. This is not the case in the present invention where two wires are available, one of these wires coming from the power supply and being connected in series with a load, the other wire coming from the load.
More particularly, the present invention relates to an electronic controller for controlling a supply of electrical power issued from a first power supply to an electrical load, comprising:
two input terminals between which said first power supply and said load can be connected in series;
an electronic switch connected between said two input terminals;
means for generating a command signal to control said supply of electrical power to said electrical load;
means for closing said electronic switch in response to said command signal to connect said two input terminals by means of said switch in such a manner that said first power supply is connected in series with said load in closed loop and thus supplies said electrical power to said load;
a second power supply for generating a power supply voltage of said electronic controller, said second power supply being derived from said two input terminals and consequently from said first power supply through said electrical load when said switch is open; and
means for opening in a temporary and repititive manner, for a whole number of power supply cycles from said first power supply, said switch in response to said command signal which normally produces a closure of said switch by said means for closing so that said power supply voltage generated by said second power supply, derived from said first power supply when said switch is open, is maintained according to an adequate standard of operation for energizing said electronic controller.
Thus, there are provided means for accumulating the sufficient energy at the controller when the commutation is open during a certain whole number of cycles of the sector power supply, and means for supplying the controller during a certain whole number of cycles of the sector power supply when the commutator is closed, this latter period being much more longer than the period for accummulating energy.
Preferably, the present invention comprises means for providing a switching only when the supply voltage of the AC line crosses zero volt to prevent transients on the line or electromagnetic interference.